1. Field of the Invention
The invention relates to an electronic silencing apparatus which reduces ambient noises in open space. This electronic silencing apparatus can be applied, for example, to a telephone set in a telephone booth at a station where many kinds of ambient noises are entering repeatedly.
2. Description of the Prior Art
FIG. 8 shows a conventional silencing apparatus for reducing the ambient noise described in the laid-open patent publication No. 2-252399 which is mounted in a telephone set for reducing the noise by electronic signal processing.
In the figure, 1 is a main body of the handset, 2 is a voice microphone, 3 is a noise microphone, 4 is a voice speaker, 5 is a voice receiving portion, 6 is an ear, 7 is an auris externa. 8 is a voice transmitting portion.
The operation of the present invention is described here. The voice microphone 2 collects the voice of the talker along with the ambient noises and transduces the acoustic signal to an electrical signal.
The noise microphone 3 collects the ambient noises and transduces the acoustic signal to an electrical signal, which is reversed in phase against the electrical signal transduced by the voice microphone, in the control circuit (not shown). These two electrical signals are added and transduced into an acoustic signal in which the ambient noises are reduced. Therefore, the voice reduced noise is outputted from the voice speaker 4. The conventional apparatus reduces the ambient noises which are passing through the auris externa 7 by eliminating the ambient noises from the received voice collected by the microphone 2.
Since the conventional silencing apparatus is constructed as described above, there is a problem that ambient noises which reach the talker's ears from the noise source except the speaker, for example, mobile noise source, cannot be reduced, although the noises generated by the speaker can be reduced.
That is, since the apparatus reduces the noise by processing the signal on the control circuit, the apparatus cannot reduce the noise transmitted in the ears of the talker through the air, although the noise included in the transmitted line can be reduced. Therefore, the talker receives ambient noises even if the noise of the speaker is reduced.
It is an object of the present invention to provide a silencing apparatus for reducing (1) an ambient noise where its position is not specified and (2) an ambient noise which is moving such as mobile noise source.
It is further object of the present invention to provide a silencing apparatus for reducing a noise within a broad area where the noise is appeared by means of collecting the noise.